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KR-7400 with a constant hum in both channels

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by nickhead, Dec 3, 2018.

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  1. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,118
    Location:
    Vancouver, WA
    Test Qk1 (2sc1419) I have seen lots of those fail shorted
     

     

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  2. nickhead

    nickhead Member

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    92
    Location:
    Elizabethtown, KY
    Yep. Lots of harsh language :) The rectifiers were good when I started, now I seem to have a problem with Dk1 and Dk3. Any idea what they can be replaced with?
     
  3. robyrony

    robyrony New Member

    Messages:
    17
    Location:
    Ireland
    Hello, I have the same receiver and it is a bit difficult to work on it only because the traces are so easy to lift from the board and break. I've replaced the two 330 ohms resistors from the power supply board with a 5 watt type, but I should have put the 25 watt (wal mount) instead because they're still getting hot. On the power amp board I've removed all the old solder and put new one. The old solder was questionable and I didn't want to take any chances. It's a lovely receiver, you just have to give it a little attention. At the end it will please your ears.
     
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  4. nickhead

    nickhead Member

    Messages:
    92
    Location:
    Elizabethtown, KY
    Has anyone replaced the diodes in these s-5151(r) cases before? It looks like they can be replaced. Thoughts?
     
  5. rjsalvi

    rjsalvi Well-Known Member

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    581
    Location:
    San Diego, CA
  6. nickhead

    nickhead Member

    Messages:
    92
    Location:
    Elizabethtown, KY
    rjsalvi,

    Mine look nothing like that. They are just 2 diodes in a metal frame (see image)
     

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  7. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    581
    Location:
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    The previous link I'd posted, is a drop in replacement ... lead spacing being the only question. Alternately, you could drop a couple pairs of these in there. The metal frame on the factory unit is a heat sink and the Mouser substitutes are so much overkill, you won't need a heat sink.

    Having said all that, you've tested the diodes out of the board and have a short? (one is oriented anode to heat sink, the other, cathode to HS)
     
  8. nickhead

    nickhead Member

    Messages:
    92
    Location:
    Elizabethtown, KY
    I just put the PS back together. I removed every component and tested them. They are all good. I think my meter batteries were dying last night and it was giving me bad readings. Anyway, the regulators are both good, the other diodes are good, the transistor is good. Everything. On the plus side I got to really clean up the solder and traces on the board and it's in much better shape now. I'm still waiting for an order to come in with the rest of the caps, but what's in there now isn't causing this issue. I got stuck on the PS board because that's where I was working. I'm pretty confident the short isn't in the PS. Now to just find it...
     
  9. nickhead

    nickhead Member

    Messages:
    92
    Location:
    Elizabethtown, KY
    Well that was easy. Qe24 is shorted every way possible and Qe22 is shorted E<-->C. Looks like I'm replacing the outputs. Anyone have any tips on getting at them? Does the whole heatsink assembly have to be removed?
     
  10. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    +1 600V 30A FREDs More than suitable, and a simple option for replacement. These original packages rarely fail though.
     
  11. nickhead

    nickhead Member

    Messages:
    92
    Location:
    Elizabethtown, KY
    They are removed easily by moving the main amp board out of the way.
     

     

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